1. Field of the Invention
This invention relates to a mechanism and a method for controlling the focal position of the UV light for auto-focussing the converged UV light, and to a method and apparatus for inspecting a device, such as a semiconductor wafer or liquid crystal, using the converged UV light.
2. Description of the Related Art
A semiconductor device is prepared by forming a fine device pattern on a semiconductor wafer. If, in the semiconductor device manufacturing process, contaminants become affixed, patten defects re produced or unusual dimensions are encountered, defects are produced in the device pattern. The semiconductor device, suffering these defects, represents a reject device, leading to lowered yield in the manufacturing process.
For stabilizing the yield in the manufacturing process at a high level, it is necessary to find pattern defects or defects ascribable to unusual dimensions, to locate the reason and to take effective measures for the manufacturing process. By locating the reason of defects to take proper measures for the manufacturing process in order to improve the yield, a new process can be started promptly to realize a high profit with the process.
If a defect is produced in the semiconductor device, the defect is searched, using a microscopic device for semiconductor inspection, to search into the reason of defects to specify the equipment or the process ascribable for the defect based on the searched results. The microscopic device for semiconductor inspection is a device, exemplified by an optical microscope, in which defects on a semiconductor wafer can be enlarged and observed, or the enlarged defect can be imaged to display the image on a monitor. Using this microscopic device for semiconductor inspection, it is possible to discriminate the nature of the defect on the defective device.
Nowadays, the design rule for the semiconductor device is prevalently 0.18 xcexcm in line width, or even finer, such that the process with the line width of 0.15 xcexcm or 0.13 xcexcm is being introduced. In keeping pace with the tendency to this fine design rule in the semiconductor process, fine defects which could be discounted in the past now raise problems, with the size of the defects to be detected being smaller.
Thus, in the conventional microscopic device for semiconductor inspection, the defects are enlarged using a light source for the visible light to observer the enlarged image. For coping with the fine design rule, a proposal has been made for a microscopic device for semiconductor inspection in which the defect is enlarged using the light source for the UV light to observe the enlarged image. By employing the UV light source, high resolution can be achieved to enable finer defects to be observed.
Since the objective lens designed for a light source for visible light does not transmit the UV light, it is necessary with the microscopic device for semiconductor inspection employing the UV light source to use a lens for UV light designed to demonstrate imaging performance optimum for the wavelength of the UV light.
However, the objective lens for the UV light, which assures high multiplication factor, the depth of focus becomes extremely short. For example, if the numerical aperture NA is 0.9, the multiplication factor is 100 and the wavelength of the UV light is 266 nm, the depth of focus is xc2x10.16 xcexcm. The focal point position of this short depth of focus is extremely difficult to adjust by a manual operation each time the inspection is to be performed. So, in the microscopic device for semiconductor inspection employing a UV light source, there is required a mechanism for making an auto-focussing accurately and speedily without relying upon a manual operation.
It is therefore an object of the present invention to provide a mechanism and a method for controlling the focal point position of the UV light in which auto-focussing of the converged UV light can be realized accurately and speedily, and a method and apparatus for inspecting a device employing the converged UV light in which auto-focussing the converged UV light can be realized accurately and speedily.
In one aspect, the present invention provides a focal point position control mechanism for UV light including supporting means for supporting an object of illumination, UV light illuminating means for illuminating UV light, converged by an objective lens, onto the object of illumination carried by the supporting means, distance detection means mounted at a fixed position with respect to the objective lens for detecting the distance to the object of illumination, and position control means for shifting the supporting means and/or the objective lens for controlling the relative position between the object of illumination and the objective lens. The position control means controls the distance between the object of illumination and the objective lens to a pre-set target distance based on the distance detected by the distance detection means.
With the present focal point position control mechanism, the objective lens and the object of illumination are moved relatively to each other, based on the distance as detected by distance detection means, the distance therebetween is used as a pre-set target distance, and the focal point position of the UV light converged by the objective lens is brought into coincidence with an optional position of the object of illumination.
In the focal point position control method for UV light according to the present invention, the distance to the object of illumination is detected by a distance detection device mounted at a fixed position relative to the objective lens. The distance between the object of illumination and the objective lens is controlled to a pre-set target distance based on the distance as detected by the distance detection device.
In the present focal point position control method for UV light, the objective lens and the object of illumination is moved relative to each other so that the distance therebetween will be a pre-set target distance. The focal point position of the UV light converged by the objective lens is brought into coincidence with an optional position of the object of illumination.
In another aspect, the present invention provides a inspection apparatus including supporting means for supporting a device, UV light illuminating means for illuminating UV light, converged by an objective lens, onto the device carried by the supporting means, distance detection means mounted at a fixed position with respect to the objective lens for detecting the distance to the device, position control means for shifting the supporting means and/or the objective lens for controlling the relative position between the device and the objective lens, UV light photographing means for detecting the reflected UV light illuminated on the device for photographing an image of the device, and inspection means for processing the image as photographed by the UV light photographing means for inspecting the device. The position control means controls the distance between the device and the objective lens to a pre-set target distance based on the distance detected by the distance detection means.
In this inspection apparatus, the objective lens and the object of illumination are moved relatively to each other so that the distance therebetween will be a pre-set target distance and so that the focal point position of the UV light converged by the objective lens will be coincident with an optional position of the object of illumination. With the present inspection apparatus, the reflected light of the UV light illuminated on the device is detected to photograph and inspect the device image.
In yet another aspect, the present invention provides an inspection method in which the UV light converged by an objective lens is illuminated on a device to detect the reflected light to inspect the device, in which the method includes detecting the distance to the device by a distance detection device mounted at a fixed position relative to the objective lens, controlling the distance between the device and the objective lens to a pre-set target distance based on the distance as detected by the distance detection device, illuminating the UV light converged by the objective lens, detecting the reflected light of the UV light illuminated on the device to photograph an image of the device and processing the image of the device as photographed for inspecting the device.
In the present inspection method, the objective lens and the object of illumination are moved relatively to each other and the distance therebetween is used as a pre-set target distance. The focal point position of the UV light, converged by the objective lens, is brought into coincidence with an optional position of the object of illumination. In this inspection method, the reflected light of the UV light illuminated on the device is detected to photograph an image of the device for inspection.
In the focal point position control mechanism and method for UV light, according to the present invention, the objective lens and the object of illumination are relatively moved, based on a distance as measured by the distance detection means or apparatus, and the distance therebetween is used as a pre-set target distance. The focal point position of the UV light converged by the objective lens is brought into coincidence with an optional position of the object of illumination.
With the focal point position control mechanism and method according to the present invention, the UV light converged by the objective lens can be auto-focussed accurately, speedily and extremely readily.
In the inspection method and apparatus according to the present invention, the objective lens and the object of illumination are relatively moved, based on a distance detected by the distance detection means and device, so that the distance therebetween will be a pre-set target distance. The focal point position of the UV light converged by the objective lens is brought into coincidence with an optional position of an object of illumination. With the present inspection method and device, the reflected light o the UV light illuminated on the device is detected to photograph and inspect he device image.
So, in the present inspection method and device, the UV light, converged by the objective lens, can be auto-focussed accurately, speedily and extremely readily to permit inspection of fine defects on a device.